1. Field of the Invention
This invention relates to an insulation-type DC-DC power conversion unit, which is appropriate for application to a charging system for an electric vehicle, and an electric system for the electric vehicle having the insulation-type DC-DC power conversion unit.
2. Description of the Related Art
FIG. 12 shows a representative drive system of a series hybrid electric vehicle. In the figure, reference numeral 1 denotes an engine, reference numeral 2 denotes a motor/generator, reference numeral 3 denotes a rectifier, reference numeral 4 denotes a main electricity storage unit for driving the vehicle, reference numeral 5 denotes an inverter, reference numeral 6 denotes an electric motor for driving the vehicle, reference numeral 7 denotes a reduction gear, reference numeral 8 denotes a differential gear, and reference numerals 9a and 9b denote wheels.
Reference numeral 10 denotes an auxiliary electricity storage unit used as a power supply of an auxiliary machine 11, reference numeral 12 denotes a charger for charging the auxiliary electricity storage unit 10 from the main electricity storage unit 4, and reference numeral 13 denotes a charger for charging the main electricity storage unit 4 from the auxiliary electricity storage unit 10. Usually, DC-DC converters are used in the chargers 12 and 13.
The voltage of the main electricity storage unit 4 is on the order of several hundred volts, while the voltage of the auxiliary electricity storage unit 10, which corresponds to a battery of an engine vehicle, is 12 V or 24 V. Thus, the chargers 12 and 13 are of electric insulation type.
The system in FIG. 12 converts mechanical energy of the engine 1 into electric energy by the dynamo (motor/generator 2) and again converts the electric energy into mechanical energy by the electric motor 6 through the rectifier 3 and the inverter 5 for driving the vehicle. This system is called series type because the energy flow is in series.
In the system, the dynamo driven by the engine 1 outputs almost constant electric power and the difference between a power generated by the motor/generator 2 and a power required for the electric motor 6 is covered by charging and discharging from the main electricity storage unit 4.
In the system as shown in FIG. 12, the motor/generator 2 are operated as the electric motor by the rectifier 3, and an electric power of the main electricity storage unit starts the engine 1 operating. Therefore, in the system, when the engine 1 is started, the electric power required for starting the engine 1 must be left in the main electricity storage unit 4.
The charger 13 is provided for the case where the electric power of the main electricity storage unit 4 is insufficient for starting the engine 1. That is, the charger 13 is operated for converting DC power of the auxiliary electricity storage unit 10 to charge the main electricity storage unit 4, and the engine 1 is started by the electric power of the main electricity storage unit 4.
After the engine 1 is started, the motor/generator 2 is caused to operate as the dynamo for charging the main electricity storage unit 4.
On the other hand, FIG. 13 shows a representative drive system of a parallel hybrid electric vehicle. Components identical with those previously described with reference to FIG. 12 are denoted by the same reference numerals in FIG. 13.
In the figure, reference numeral 100 denotes an engine, reference numerals 102a and 102b denote clutches, reference numeral 103 denotes a motor/generator, reference numeral 101 denotes a rectifier, and reference numeral 104 is a reduction gear. The clutch 102a is used to disconnect power of the engine 100 and the clutch 102b is provided for the reduction gear 104 like that used with an engine vehicle.
The system, which is called a torque assist system, is one kind of parallel system. It enables the engine 100 solely to drive the vehicle and also enables the motor/generator 103 solely to drive the vehicle electrically.
To drive the vehicle by the engine, an output of the engine 100 is inputted via a shaft of the motor/generator 103 to the reduction gear 104 for driving wheels 9a and 9b, and the motor/generator 103 operates as a dynamo for charging a main electricity storage unit 4 through the rectifier 101. To drive the vehicle electrically, the engine 100 is disconnected by the clutch 102a and the rectifier 101 is operated in an inverter mode by an electric power of the main electricity storage unit 4, thereby operating the motor/generator 103 as an electric motor. This operation method becomes similar to a method in the series system.
To start the engine 100, the clutch 102b is disconnected, the clutch 102a is connected, and the motor/generator 103 is operated as the electric motor. This method is also similar to the method in the series system.
FIG. 14 shows a drive system of a battery-operated electric vehicle. Components identical with those previously described with reference to FIGS. 12 and 13 are denoted by the same reference numerals in FIG. 14.
In FIG. 14, reference numeral 40 denotes a main electricity storage unit (main battery) for driving the vehicle, reference numeral 50 denotes an inverter, reference numeral 60 denotes an electric motor for driving the vehicle, and reference numeral 70 denotes a reduction gear. An electric vehicle having a battery as a power source can not continue to run if the electric power of the battery becomes insufficient. However, if such a situation occurs, it is necessary that the vehicle should be able to be moved to a safety place. Thus, a charger 13 is installed for charging an electric power of an auxiliary electricity storage unit 10 to the main electricity storage unit 40, and the vehicle is run and moved by the electric power of the main electricity storage unit 40.
FIG. 15 shows the circuit configuration of the charger 12 of the auxiliary electricity storage unit 10 shown in FIGS. 12 to 14. Here, a representative insulation-type bi-directional DC-DC converter is used as the charger 12.
In FIG. 15, reference numeral 120 denotes an input smoothing capacitor, reference numerals 121P and 121N denote semiconductor switches, reference numeral 122 denotes an insulating transformer having a primary side connected between the semiconductor switches 121P and 121N in series, reference numeral 122P denotes a primary winding of the insulating transformer 122, reference numeral 122S denotes a secondary winding of the insulating transformer 122, reference numerals 123P and 123N denote free-wheeling diodes connected between both ends of the capacitor 120 and both ends of the primary winding 122P, reference numerals 124 and 125 denote output rectifier diodes connected to both ends of the secondary winding 122S, reference numeral 126 denotes an output smoothing reactor, and reference numeral 127 denotes an output smoothing capacitor.
The operation of the circuitry in FIG. 15 will be described with reference to FIG. 16.
As shown in FIG. 16, the semiconductor switches 121P and 121N are turned on/off at the same time. In the figure, T denotes an operation period of the switches; Ton denotes an on period and Toff denotes an off period. The ratio of the on period Ton to the period T is controlled, whereby the charge current for the auxiliary electricity storage unit 10 is controlled.
FIG. 17 shows the circuit configuration of the charger 13 of the main electricity storage unit 4 or 40 shown in FIGS. 12 to 14. Here, a representative insulation-type bi-directional DC--DC converter is used as the charger 13.
In FIG. 17, reference numeral 130 denotes an input smoothing capacitor, reference numerals 131P and 131N denote semiconductor switches, reference numeral 132 denotes an insulating transformer having a primary side connected between the semiconductor switches 131P and 131N in series, reference numeral 132P denotes a primary winding of the insulating transformer 132, reference numeral 132S denotes a secondary winding of the insulating transformer 132, reference numerals 133P and 133N denote free-wheeling diodes which are connected between both ends of the capacitor 130 and both ends of the primary winding 132P, reference numerals 134 and 135 denote output rectifier diodes connected to both ends of the secondary winding 132S, reference numeral 136 denotes an output smoothing reactor, and reference numeral 137 denotes an output smoothing capacitor.
Putting the circuit configuration in FIG. 17 in contrast with that in FIG. 15, the circuitry in FIG. 17 results from inverting the input and output of the circuitry in FIG. 15; both circuit configurations are symmetrical and substantially the same and therefore the operation of the circuitry in FIG. 17 will not be described again.
The charger 13 shown in FIG. 17 charges the main electricity storage unit 4 or 40.
As shown in FIGS. 12 and 13, in the hybrid electric vehicle having the engine started by the electric power of the main electricity storage unit 4, the charger 13 in the case of emergency for charging the main electricity storage unit 4 from the auxiliary electricity storage unit 10 is provided aside from the service charger 12 for charging the auxiliary electricity storage unit 10 from the main electricity storage unit 4 so that the electric power of the auxiliary electricity storage unit 10 can be used to start the engine.
As shown in FIG. 14, the electric vehicle which runs only with the electric power of the main electricity storage unit 40 also comprises the charger 13 such as the above which is provided for the case where the electric power of the main electricity storage unit 40 is exhausted and the vehicle becomes impossible to run.
Thus, each of the electric vehicles including the hybrid electric vehicles comprises the emergency charger for the main electricity storage unit in addition to the service charger for the auxiliary electricity storage unit, resulting in upsizing, increase in weight, high cost, and the like of in-car machine, which are to be solved.